Add PyMySQL python library for SQL Reporter support

It doens't have any other dependencies, but it's an optional depend for
Zuul itself, because plugins. Install it for the scheduler. Also,
provide an option flag to enable it.

Change-Id: I4cad419598ffefcdca5161664c6d073da37fb42f

manifests/scheduler.pp

@@ -19,7 +19,29 @@ class zuul::scheduler (
   $ensure = undef,
   $layout_dir = '',
   $manage_log_conf = true,
+  $python_version = 2,
+  $use_mysql = false,
 ) {
+
+  include ::pip
+
+  if ($use_mysql) {
+      if ($python_version == 3) {
+        include ::pip::python3
+        $pip_provider = pip3
+        $pip_command = 'pip3'
+      } else {
+        $pip_provider = openstack_pip
+        $pip_command = 'pip'
+      }
+
+      package { 'PyMySQL':
+        ensure   => present,
+        provider => $pip_provider,
+        require  => Class['pip'],
+      }
+  }
+
   if ($::operatingsystem == 'Ubuntu') and ($::operatingsystemrelease >= '16.04') {
     # This is a hack to make sure that systemd is aware of the new service
     # before we attempt to start it.